This application relates generally to servo control systems and more particularly to a method and apparatus that measures servo data for one track while calculating values for another track.
Disc drives have magnetic discs that are rotated while read and write heads communicate magnetic signals to and from the rotating disc. The magnetic signals are generally written in tracks that often form generally concentric circles about the magnetic disc. The tracks periodically contain servo related data, such as a track ID that indicates the track that the head is positioned over as well as position data that indicates the radial position of the head relative to other tracks and the centerline of the current track. Servo bursts are written into the magnetic disc during manufacturing and contain the servo related data.
A servo control system positions the head over the desired track and maintains that position during the read or write process for the desired track. The servo control system utilizes the servo related data to maintain the head""s position over the desired track by detecting that the head is straying from the centerline and by applying correction to the head""s position. However, the servo related data initially written during manufacturing may result in eccentricities, referred to as repeatable run out (RRO), due to various reasons such as spindle motor harmonics. Furthermore, the servo control system""s response may introduce additional eccentricity. As a result, the head follows tracks that are not ideally concentric.
The eccentricity of the tracks may create problems because one track may encroach upon another and data stored on the disc could become corrupt due to overwriting. Ideal track centerlines follow concentric paths that prevent such encroachment. Therefore, to establish the concentric path, a zero acceleration path (ZAP) is computed during certification of the disc drive. The ZAP process reads the servo data resulting in eccentricities and computes corrections that are written into the ID field of the track sectors for both the read heads and the write heads. These corrections instruct the servo control system to maintain the head such that generally concentric tracks result.
ZAP reduces the eccentricities but requires a relatively large amount of time to perform per disc drive being certified. Conventionally, ZAP is performed by reading servo data from a track, averaging position errors from an ideal center, and computing corrections based on the position error data. The corrections are then written into the ID fields for the track. This set of serial operations is repeated for each track and for each head.
Accordingly there is a need for a method that decreases the amount of time necessary for performing ZAP.
Against this backdrop the present invention has been developed. The present invention involves measuring servo data for one track while calculating the correction servo data for a previously measured track and then returning to the previously measured track to write the correction servo data. The time spent calculating for one track and measuring for another is thereby combined into the same time period to reduce the overall length of time require by ZAP.
An exemplary method for simultaneously measuring and calculating servo related data in a disc drive includes the following steps. A first servo related data is measured from a first track. Then, a second servo related data is measured from a second track. While performing the measuring step for the second track, a servo related value is calculated for the first track based on the first servo related data.
An exemplary disc drive configured to perform the exemplary method for simultaneously measuring and calculating servo related data includes the following elements. At least one head having a controllable position is included. The head is configured to perform the measuring steps of the method. A processor is included and is configured to receive servo related data from the head and to perform the calculating step of the method. A servo control is also included and is configured to control the position of the head.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.